Multifocal ophthalmic lens

ABSTRACT

A multifocal ophthalmic lens, having outer annular zones with vision correction powers less than a far vision correction power of the patient, is disclosed. These additional annular zones come into play, when the pupil size increases under dim lighting conditions, to thereby compensate for the near-vision powered annular zones. The net effect of the additional near vision annular zones and the additional annular zones having power less than the far vision correction power is to shift the best quality image from in front of the retina to an area on the retina of the eye, to thereby reduce halo effects and improve image contrast.

This is a division of application Ser. No. 09/221,558, filed Dec. 28,1998, now U.S. Pat. No. 6,221,105, which is a division of applicationSer. No. 08/885,987 filed Jun. 30, 1997, now U.S. Pat. No. 5,919,229,which is a division of application Ser. No. 08/592,752 filed Jan. 26,1996, now U.S. Pat. No. 5,702,440.

FIELD OF THE INVENTION

The present invention relates generally to ophthalmic lenses and, moreparticularly, to a multifocal ophthalmic lens adapted for implantationin an eye, such as an intraocular lens, or to be disposed in a cornea,such as a corneal inlay.

BACKGROUND OF THE INVENTION

The general construction of a multifocal ophthalmic lens is known in theart. U.S. Pat. No. 5,225,858, which is incorporated herein by reference,discloses a multifocal ophthalmic lens including a central zonecircumscribed by multiple concentric, annular zones. This patentdiscloses a means of providing improved image quality and lightintensity for near images. The improved image quality is accomplished bymaintaining the near vision correction power of appropriate zones of thelens substantially constant for a major segment of the near visioncorrection power region of each zone, and by providing a central zonehaving an increased depth of focus.

The major segment of each near vision correction power region, which hasa substantially constant near vision correction power, inherentlyreduces the depth of focus associated with far vision. The location ofnear focus is typically immaterial for near vision, because of theability of the user to easily adjust the working distance of the targetobject. The patent discloses progressive vision correction powers in thecentral zone for extending the depth of focus. The increased depth offocus provided by the central zone helps to compensate for the reductionin depth of focus associated with the near vision correction powerregions. This feature is particularly applicable to an intraocular lens,since the patient has minimal residual accommodation, i.e., the abilityof a normal eye to see objects at different distances.

FIG. 1 shows how the multifocal ophthalmic lens 6 of the prior artfocuses parallel incoming light onto the retina 10 of the eye. For thenormal lighting condition with a 3 mm pupil diameter, the rays 7 passthrough a far focus region of the multifocal ophthalmic lens 6, and arefocused onto the retina 10. The rays 8 pass through a near region of themultifocal ophthalmic lens 6, and are focused into a region between theretina 10 and the multifocal ophthalmic lens 6.

The multifocal ophthalmic lens 6 shown in FIG. 1 shows the passage ofparallel rays through the multifocal ophthalmic lens 6 in a well-litenvironment. In low lighting conditions, the pupil enlarges, andadditional annular zones of the multifocal ophthalmic lens 6 becomeoperative to pass light therethrough. These additional annular regionsoperate to provide additional far (rays 10 in FIG. 1) and near-focuscorrective powers to the multifocal ophthalmic lens 6. Presence of theadditional intermediate and near rays shift the best image quality forfar vision to the location in front of the retina. As a result, in lowlighting conditions the best quality image of the multifocal ophthalmiclens 6 appears in a region slightly in front of the retina 7. A userlooking through the multifocal ophthalmic lens 6 while driving at night,for example, may notice an undesirable halo affect around a brightsource of light. The shift in the best quality image just in front ofthe retina 7 instead of on the retina 7 increases the halo effect makingdriving for some people difficult.

A problem has thus existed in the prior art of providing a multifocalophthalmic lens, which can provide a desirable far vision correction inlow lighting conditions, but which does not unnecessarily elevate halosand contrast reductions under increased pupil size which usually occursin low lighting conditions. Thus, the prior art has been unable toproduce a multifocal ophthalmic lens, which achieves a best qualityimage on the retina (instead of slightly in front of the retina) in lowlighting conditions.

Under low lighting conditions, the best quality image of prior artmultifocal ophthalmic lenses is not focused on the retina of the eye.Instead, these prior art multifocal ophthalmic lenses have a bestquality image in front of the retina in low lighting conditions, whichcorresponds to a mean power of the multifocal ophthalmic lens beingslightly higher than the far vision correction power required for thepatient.

SUMMARY OF THE INVENTION

As light diminishes and pupil size correspondingly increases, the outerannular zones of a multifocal ophthalmic lens begin to pass lighttherethrough. These outer annular zones traditionally introduceadditional near vision correction power, which effectively shifts thebest quality image from on the retina to an area slightly in front ofthe retina.

The outer annular zones of the present invention have vision correctionpowers, which are less than the far vision correction power of thepatient, to compensate for the increase in the mean power of themultifocal ophthalmic lens. A multifocal ophthalmic lens, having outerannular zones with vision correction powers less than a far vision powerof the patient, is disclosed. The additional annular zone or zones comeinto play when the pupil size increases under dim lighting conditions,to thereby compensate for the additional near vision annular zonesintroduced by the enlarged pupil size. The net effect of the additionalnear vision annular zones and the additional annular zones having powerless than the far vision correction power is to focus the best qualityimage onto the retina of the eye, to thereby reduce halo effects andimprove contrast.

The multifocal ophthalmic lens of the present invention is adapted to beimplanted into an eye or to be disposed in a cornea, and has a baselinediopter power for far vision correction of the patient. The multifocalophthalmic lens includes a central zone having a mean vision correctionpower equivalent to or slightly greater than the baseline diopter powerdepending upon pupil size, and includes a first outer zone locatedradially outwardly of the central zone.

A second outer zone located radially outwardly of the first outer zoneprovides vision correction power, that is less than the baseline diopterpower. The vision correction power of the second outer zone can besubstantially constant. Light generally does not pass through the secondouter zone under bright lighting conditions.

A third outer zone of the multifocal ophthalmic lens comes into play inlower lighting conditions, and includes a vision correction powergreater than the baseline diopter power. A fourth outer zonecircumscribes the third outer zone, and includes a vision correctionpower, that is less than the baseline diopter power. This fourth outerzone passes light in very low lighting conditions, when the pupil issignificantly dilated. The second and fourth outer zones serve to focuslight slightly behind the retina of the eye, to thereby compensate forlight focused in front of the retina of the eye by the first and thirdouter zones, under dim lighting conditions.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view illustrating the focusing of light of a priorart multifocal ophthalmic lens onto a retina;

FIG. 2 is a plan view of an intraocular multifocal ophthalmic lens ofthe presently preferred embodiment;

FIG. 3 is a side elevational view of the intraocular multifocalophthalmic lens of the presently preferred embodiment;

FIG. 4 is a plot of the power of the optic versus distance from theoptic axis for the intraocular multifocal ophthalmic lens of thepresently preferred embodiment;

FIG. 5 is a schematic view illustrating the focusing of light of theintraocular multifocal ophthalmic lens of the presently preferredembodiment onto a retina.

These and other aspects of the present invention are apparent in thefollowing detailed description and claims, particularly when consideredin conjunction with the accompanying drawings in which like parts bearlike reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 2 and 3 show an intraocular lens 11, which comprises a circularoptic 13 and two fixation members 15 and 17. The optic 13 may beconstructed of rigid biocompatible materials, such aspolymethylmethacrylate (PMMA), or flexible, deformable materials, suchas silicone, hydrogel and the like which enable the optic to be rolledor folded for insertion through a small incision into the eye.

In the presently preferred embodiment, the fixation members 15 and 17are fine hair-like strands or filaments which are attached to the optic13 using conventional techniques. The fixation members 15 and 17 may beconstructed of a suitable polymeric material, such as PMMA orpolypropylene. Alternatively, the fixation members 15 and 17 may beintegral with the optic 13. The optic 13 and the fixation members 15 and17 may be of any desired number and configuration, and theconfigurations illustrated are purely illustrative.

The optic 13 has a central zone 18, inner and outer annular near zones19 and 20, and an annular far zones 21 and 22. In the presentlypreferred embodiment, the central zone 18 is circular, and theperipheries of the annular zones 19-22 are circular. The annular zones19-22 circumscribe the central zone 18, and the zones are contiguous.The zones 19-22 are concentric and coaxial with the optic 13.

The zones 18-22 are used in describing the vision correction power ofthe optic 13, and they are arbitrarily defined. Thus, the peripheries ofthe zones 18-22 and the number of zones may be selected as desired.However to facilitate describing the optic 13, the peripheries of theannular zones 19-22 are considered to be the zero crossings in FIG. 4.Although the boundaries of the zones 18-22 are indicated by phantomlines in FIG. 2, it should be understood that the optic 13 has no suchlines in any of its surfaces and that these lines constitute referencelines which define the zones.

As shown in FIG. 3, the optic 13 has a convex anterior surface 25 and aplanar posterior surface 27; however, these configurations are merelyillustrative. Although the vision correction power may be placed oneither of the surfaces 25 and 27, in the presently preferred embodiment,the anterior surface 25 is appropriately shaped to provide the desiredvision correction powers.

FIG. 4 shows the preferred manner in which the vision correction powerof the optic 13 varies from the center or optical axis 29 of the optic13 to the circular outer periphery 31 of the optic. A preferred powerdistribution curve for a corneal inlay may be similar, or identical, tothe curve of FIG. 4.

In FIG. 4, the vertical or “Y” axis represents the variation in diopterpower of the optic 13 from the baseline or far vision correction power,and the “X” or horizontal axis shows the distance outwardly from theoptical axis 29 in millimeters. Thus, the zero-diopter or baseline powerof FIG. 4 is the power required for far vision for a conventionalmono-focal intraocular lens. The power variation shown in FIG. 4 isapplicable to any radial plane passing through the optical axis 29. Inother words, the power at any given radial distance from the opticalaxis 29 is the same.

The central zone 18 extends from the optical axis 29 to a circularperiphery 33, the first annular near zone 19 is considered as extendingfrom the periphery 33 to a circular periphery 34, and the outer annularnear zone 20 is considered as extending from a periphery 35 to aperiphery 36. The negative diopter power of the two zones 21, 22 are ofless power than required for far vision and may be considered as far,far vision correction powers. The annular far, far zone 21 extendsbetween the peripheries 34 and 35, and the annular far, far zone 22extends from the periphery 36 radially outwardly to the outer periphery31 of the optic 13. As shown in FIG. 4, the vision correction powercrosses the “X” axis or baseline at the peripheries 33, 34, 35 and 36.

As shown in FIG. 4, the vision correction power varies progressively andcontinuously from a baseline diopter power at the optical axis 29 to anapex 38 and then decreases continuously and progressively from the apex38 back through the baseline diopter power to a negative diopter powerat a point 39. From the point 39, the vision correction power increasescontinuously and progressively through the periphery 33 into the innerannular near zone 19. Of course, the diopters shown on the ordinate inFIG. 4 are merely exemplary, and the actual correction provided willvary with the prescription needs of the patient.

The apex 38 has a vision correction power for intermediate vision. Theintermediate vision correction powers may be considered as being in azone 40 which may be between 0.5 and 0.75 diopters from the baselinediopter power, as presently embodied. The far vision correction powersmay be considered as lying between the zone 40 and the baseline dioptercorrection, and the far, far vision correction powers are negative. Theintermediate, far, and far, far powers combine to provide a mean powerin the central zone 18.

Within the inner annular near zone 19, the vision correction powervaries continuously and progressively from the periphery 33 to a plateau41; and from the plateau 41, the vision correction power variescontinuously and progressively back to the periphery 34 at the baseline.

In the far, far zone 21 the vision correction power is below the farzone correction power, and is substantially constant. This visioncorrection power returns to the baseline at the periphery 35.

In the outer annular near zone 20, the power varies continuously andprogressively from the periphery 35 to a plateau 45, and returnscontinuously and progressively from the plateau 45 to the baseline atthe periphery 36.

In the far, far zone 22, the vision correction power is substantialconstant, below the baseline vision correction power. The substantiallyconstant vision correction power of the far, far zone 22 is slightlylower than the substantially constant vision correction power of thefar, far zone 21, as presently embodied. The vision correction power ofthe far, far zone 22 remains negative from the periphery 36 to thebaseline correction power at the outer periphery 31.

The inner near zone 19 has regions adjacent the peripheries 33 and 34with far vision correction powers and a second region, which includesthe plateau 41, with near vision correction powers. Similarly, the outernear zone 20 has regions adjacent the peripheries 35 and 36 with farvision correction powers and a second region, which includes the plateau45, with near vision correction powers. For example, the near visionpowers may be those which are above 2 or 2.5 diopters. The 2 to 2.5diopters correspond to about 20 to 15 inches, respectively, of workingdistance, and this distance corresponds to the beginning of nearactivities. The two far, far vision correction plateaus 42, 43 of thetwo far, far annular zones 21, 22, respectively, preferably comprisediopter powers approximately one fifth of the distance between thebaseline and the plateaus 41, 45, but located below the baseline.

As shown in FIG. 4, each of these “near” regions has a major segment,i.e., the plateaus 41 and 45 in which the near vision correction poweris substantially constant. The plateau 41, which lies radially inwardlyof the plateau 45, has a greater radial dimension than the plateau 45.The difference in radial dimension of the plateaus 41 and 45 allowsthese two plateaus to have approximately the same area.

Only a relatively small portion of the anterior surface 25 (FIG. 3) isdedicated to intermediate vision powers. This can be seen by therelatively small radial region which corresponds to the intermediatezone 40 (FIG. 4) and by the rapid change in diopter power between theplateaus 41 and 45 and the baseline diopter axis.

The diagrammatic view of FIG. 5 shows how the multifocal ophthalmic lens13 of the present invention focuses parallel light onto a retina 10 ofthe eye, in dim lighting conditions. The parallel rays 50 pass throughthe central portion 18 of the multifocal ophthalmic lens 13, and arefocused onto the retina 10. The rays 51 pass through the intermediatefocus region 40 of the central zone 18, and are focused in an areabetween the retina 10 and the multifocal ophthalmic lens 13. The rays 52pass through the plateau 41 of the near zone 19 and, depending upon thelighting conditions, pass through the plateaus 42, 43 of the two far,far zones 21, 22, and the plateau 45 of the near zone 20. These rays 52are focused slightly behind the retina 10. In the presently preferredembodiment, the distance at which the rays 52 are focused behind theretina 10, is approximately one-fifth of the distance at which the rays51 are focused in front of the retina 10. The combination of the rays50, 51, and 52 combine to form a best quality image on the retina 10 indim lighting conditions.

While this invention has been described with respect to various specificexamples and embodiments, it is to be understood that the invention isnot limited thereto and that it can be variously practiced within thescope of the following claims.

What is claimed is:
 1. A multifocal intraocular lens for providingvision correction power, the multifocal intraocular lens having acentral optical axis, an outer periphery and a baseline diopter powerfor far vision correction, the multifocal intraocular lens being sizedand structured to be implanted in an eye, and comprising: a central zonehaving a vision correction power at the central optical axis no lessthan the baseline diopter power and a vision correction powerapproximately equal to or greater than the baseline diopter power, thecentral zone having a progressive power region in which the visioncorrection power varies progressively; a first zone having a near visioncorrection power, the first zone being located radially outwardly of thecentral zone; and a second zone located radially outwardly of the firstzone and extending to the outer periphery of the multifocal intraocularlens and having a vision correction power less than the baseline diopterpower substantially throughout the second zone.
 2. The multifocalintraocular lens according to claim 1, wherein the first zone is annularand circumscribes the central zone, and the second zone is annular andcircumscribes the first zone.
 3. The multifocal intraocular lensaccording to claim 1, wherein the vision correction power of the secondzone is substantially constant throughout.
 4. The multifocal intraocularlens according to claim 2, wherein the vision correction power of thesecond zone is substantially constant throughout.
 5. The multifocalintraocular lens according to claim 1, wherein the vision correctionpower at the central optical axis is approximately the baseline diopterpower.
 6. The above-identified application has been carefully reviewedclaim 5, wherein the first zone is annular and circumscribes the centralzone, and the second zone is annular and circumscribes the first zone.7. The multifocal intraocular lens according to claim 5, wherein thevision correction power of the second zone is substantially constantthroughout.